1. Field of the Invention
The present invention relates to a replaceable orifice unit, and more particularly to a replaceable orifice unit for controlling the flow rate of a high purity chemical or any other fluid in a fluid circuit used in semiconductor fabrication process, for example, wherein the replaceable orifice unit is disposed outside a pressure or a flow regulator valve in the fluid circuit.
2. Description of the Related Art
Heretofore, it has been known in the art of semiconductor fabrication to use an orifice unit outside a pressure or a flow regulator valve in regulating the flow rate of a fluid in a fluid circuit, and also known to use a pressure or a flow regulator valve in which the orifice unit is incorporated. The orifice unit thus incorporated in the regulator valve is hereinafter referred to as “incorporated-type orifice unit.
Essentially, the pressure or the flow regulator valve functions to keep constant both the fluid pressure and the flow rate of the fluid in a downstream side of the pressure or the flow regulator valve, independent of variations of the fluid in both fluid pressure and flow rate in an upstream side of the pressure or the flow regulator valve in the fluid circuit. Further, it is known in the art to stabilize the flow rate of the fluid in the downstream side of the pressure or the flow regulator valve by imposing a suitable load on the downstream side of the pressure or the flow regulator valve, wherein the load is realized in the form of either a fixed orifice unit or an adjustable orifice unit an orifice of which is adjustably sized using a needle member.
In controlling the flow rate of a fluid in a fluid circuit, it is also known to control the pressure or the flow regulator valve in the fluid circuit by using a thumbscrew of a main body of the regulator valve when the regulator valve is of a manually controlled type, and also known to control the pressure or the flow regulator valve in the fluid circuit by using a variable pilot pressure of the regulator valve when the regulator valve is of an air or pneumatically operated type. Furthermore, it is also known in the art to control the pressure or the flow regulator valve by changing a fixed orifice unit or by controlling a needle valve in the downstream side of the pressure or the flow regulator valve.
However, in the case of the needle valve, the flow rate of the fluid in the circuit having been once set by using the needle valve tends to vary and is therefore poor instability or reliability. Due to this, the fixed orifice unit is widely used in the art as a load imposed on the downstream side of the pressure or the flow regulator valve in the fluid circuit. In using the fixed orifice unit in the downstream side of the pressure or the flow regulator valve in the fluid circuit, as described above, there are two possible cases. Namely, in one of these possible cases, the fixed orifice unit is incorporated in the main body of the pressure or the flow regulator valve. This satisfies less space requirement in the fluid circuit. On the other hand, in the other possible case, in order to simplify the pressure or the flow regulator valve in maintenance service in the fluid circuit, the fixed orifice unit may be of a replaceable type disposed outside the pressure or the flow regulator valve in the fluid circuit.
In using the fixed orifice unit, it is possible for the pressure or the flow regulator valve to satisfy the less space requirement in the fluid circuit by having the fixed orifice unit incorporated in the pressure regulator valve when the flow rate of the fluid in the fluid circuit is previously determined. This, however, makes it difficult for the pressure or the flow regulator valve to meet various requirements in performance when the fluid circuit is changed in design. Further, in doing maintenance service on the pressure or the flow regulator valve in the fluid circuit, it is necessary to dismount the pressure of the flow regulator valve from the fluid circuit. Further, in order to do maintenance service on the fixed orifice unit thus incorporated in the pressure or the flow regulator valve, it is necessary to disassemble the entire pressure or the entire flow regulator valve. Due to this, maintenance on the fixed orifice unit thus incorporated in the regulator valve is very cumbersome and time-consuming labor service.
As for a replaceable orifice unit, it is possible to simplify maintenance service on such a replaceable orifice unit. However, the replaceable orifice unit is relatively large in size. This makes it difficult to down-size a fluid circuit which employs the replaceable orifice unit as one of its component. More specifically, FIG. 4 shows a replaceable orifice unit 31 of a conventional type assuming a block-like shape. As is clear from FIG. 4, the conventional replaceable orifice unit 31 has an upstream side and a downstream side. In the upstream side of the conventional replaceable orifice unit 31, there is provided an upstream connecting tube unit 32 having its opposite end portions fixedly connected with a pair of an upstream and a downstream coupling unit. Through the upstream coupling unit, the upstream connecting tube unit 32 is fluid-communicated with the pressure or the flow regulator valve 33. Further, in the downstream side of the replaceable orifice unit 31, as is clear from FIG. 4, there is provided a downstream connecting tube unit 34 having its opposite end portions fixedly connected with a pair of an upstream and a downstream coupling unit. Through the downstream coupling unit, the downstream connecting tube unit 34 is fluid-communicated with an air or pneumatically operated valve 35. Since the conventional replaceable orifice unit 31 has the above construction, the conventional replaceable orifice unit 31 is too bulky as a whole in the fluid circuit.
Further, since any type of orifice units is bought into contact with a chemical flowing through the fluid circuit in operation, it is necessary for any type of the orifice units to have its inner wall lined with a specialized and therefore expensive chemical-resistance substance. This increases the manufacturing cost of the fluid circuit employing any type of the orifice units.
Consequently, a need exists in the art for entire replacement of the orifice unit in the fluid circuit. As for the orifice unit of a replaceable type, it is possible to do maintenance service on the replaceable orifice unit in an easy manner by simply replacing the connecting tube units 32, 34 of the opposite ends of the replaceable orifice unit 31 together with the replaceable orifice unit 31 itself with a set of new connecting tube units 32m 34 and a new replaceable orifice unit 31. However, this forces a user to keep ready on hand a plurality of extra sets of both the connecting tube units 32, 34 and the replaceable orifice units 31, and is therefore disadvantageous from an economical point of view. In view of this economical disadvantage, in ordinary maintenance service of the replaceable orifice unit 31 of a conventional type, only an orifice plate 36 (shown in FIG. 6) of the conventional replaceable orifice unit 31 is replaced with a new one 36 in the art.
Further, in the conventional orifice unit of either a replaceable type 31 or an incorporated type, as shown in FIGS. 5 and 6, the orifice plate 36 having its orifice 37 reduced in diameter extends in a direction perpendicular to a flow direction of the fluid in the fluid circuit. Due to this, in the conventional orifice unit 31, as is clear from FIG. 6, there is a fear that impurities 38 of the fluid, for example, such as dust, debris and like impurities 38 bank up against the upstream side of the orifice plate 36 inside an inner wall of the conventional orifice unit 31. The impurities 38 thus deposited on the inner wall of the conventional orifice unit 31 adjacent to the upstream side of the orifice plate 36 tend to significantly impair the conventional orifice unit 31 in performance in the fluid circuit.